1. Field of the Invention
The present invention relates to a recording or reproducing apparatus, and, more particularly, to a stabilizing member (pad) serving as an interface to stabilize a condition of contact between a recording or reproducing head and a recording medium.
2. Description of the Prior Art
Hitherto, a recording or reproducing apparatus capable of recording information on or reproducing information from a sheet recording medium such as a flexible magnetic disk has been known.
In an apparatus of the type described above, the running magnetic sheet has been able to stably come in contact with the magnetic head by hydrodynamical pressure generated by a stabilizing plate (pad) which generates the pressure in association with the rotational action of the magnetic sheet.
A pad of the type described above has been disclosed as shown in FIG. 1. That is, a pad 101 is fastened to surround a magnetic head 100, the pad 101 having a space (recessed groove) 101a capable of generating hydrodynamical negative pressure on a surface thereof which confronts the magnetic sheet, the hydrodynamical negative pressure attracting the magnetic sheet to the magnetic head 100 due to the rotation of the magnetic sheet. Furthermore, the pad 101 further comprises a projection portion 101b on the periphery thereof, the projection portion 101b forming the above-described space (recessed groove). In addition, a cut portion 101d is formed at a position on the edge of the pad 101 downstream in the direction of rotation of the magnetic sheet, the cut portion 101d enabling air to flow out.
The magnetic head 100 is disposed so as to project upwards through a central opening 101c formed in the pad 101.
A negative pressure pad of the type described above is arranged to act in such a manner that, when the magnetic sheet is rotated, air in the above-described space and confronting the magnetic sheet flows out through a gap formed between the projection portion and the magnetic sheet and through the cut portion formed in the surface of the projection portion. In addition, since substantially no air flows into the gap between the projection portion and the magnetic sheet, negative pressure is generated in the above-described space and the gap between the projection portion and the magnetic sheet. As a result, the magnetic sheet is attracted by the negative pressure thus generated so as to closely contact the magnetic head.
The above-described conventional negative pressure pad usually has been arranged in such a manner that the depth of the groove portion 101a is uniform. The results of the hydrodynamical analysis of the distribution of the negative pressure generated between the negative pressure pad and the magnetic sheet are designated by curve 1.sub.2 shown in FIG. 5. Referring to FIG. 5, positions denoted by symbols P1 to P8 correspond to the positions P1 to P8 of the surface of the pad 101 shown in FIG. 1 which confront the magnetic sheet. As is shown, the level of the negative pressure at the inner portion is lower than that at the outer portion.
As described above, the conventional negative pressure pad has a problem in that the levels of the negative pressure generated in the inner portion of the disk (magnetic sheet) and the outer portion of the same become considerably different from each other due to the difference in the peripheral velocity between the two portions. That is, since the inner portion of the disk rotates more slowly than the outer portion, the force for attracting the disk becomes weak in the inner portion. This condition is amplified, since the inner portion is more rigid than the outer portion of the disc, because of the disk having a center core in the center portion thereof. Therefore, the inner portion of the disk cannot be easily deformed in comparison to the outer portion of the same. As a result, in a case when, for example, a frame recording head is utilized in which an excellent head touch is desired over a wide area, a problem arises in that the desired head touch cannot be obtained due to the insufficient level of the negative pressure in the inner portion. If negative pressure of an excessive level is applied, a problem arises in that the spindle motor suffers from an excessively large load. What is even worse is that the disk will vibrate due to the attractive force and the restoring force of the disk, causing jitter to be generated. Furthermore, if the rotational speed of the spindle motor is changed, recording or reproducing cannot be correctly performed.